[mediaman]

Out of curiosity, did you try this in o3?

O3's web research seems to have gotten much, much better than their earlier attempts at using the web, which I didn't like. It seems to browse in a much more human way (trying multiple searches, noticing inconsistencies, following up with more refined searches, etc).

But I wonder how it would do in a case like yours where there is conflicting information and whether it picks up on variance in information it finds.

[SpicyLemonZest]

I just asked o3 how to fill out a form 8949 for a sale with an incorrect 1099-B basis not reported to the IRS. It said (with no caveats or hedging, and explicit acknowledgement that it understood the basis was not reported) that you should put the incorrect basis in column (e) with adjustments in (f) and (g), while the IRS instructions are clear (as much as IRS instructions can be...) that in this scenario you should put the correct basis directly in column (e).